How can I hide a calendar without deleting it?

To hide a calendar from view without deleting it, you can unsubscribe from it by double-clicking on the calendar in the left sidebar to show the Calendar Info dialog and click the Unsubscribe button. Then choose Hide Unsubscribed Calendars from the View menu to hide it from view.

To later re-subscribe to the calendar, simply click on the checkbox button next to the calendar name. If it's not visible, click on the View Menu > Show Unsubscribed Calendars.